Naturally ventilating rooms is a great low carbon building design strategy, however care needs to be taken to ensure that the occupants will receive a sufficient amount of fresh air. With an insufficient amount of fresh air carbon dioxide levels within the rooms will increase, the room will feel stuffy and the occupants will start to become drowsy.
To ensure that the carbon dioxide levels are kept to a minimum, different industry standards recommend slightly different natural ventilation levels. The industry standard you will need to meet will depend on the type of building being built. You can find out more about the different industry standards below.
Ventilation should be provided to limit the concentration of carbon dioxide in all teaching and learning spaces. When measured at seated head height, during the continuous period between the start and finish of teaching on any day, the average concentration of carbon dioxide should not exceed 1500 parts per million (ppm).
Building Bulletin 101 (BB 101) advises that new school teaching and learning spaces that are to be naturally ventilated must have the capability of achieving a minimum of 8 l/s per person at any occupied time.
The PSBP recently superseded the requirements of BB 101 (although many Building Control and Planning Departments still ask for schools to meet BB 101). The PSBP states that ventilation should be provided to limit the concentration of carbon dioxide measured at seated head height in all teaching and learning spaces.
Where natural ventilation is used or when hybrid or mixed mode systems are operating in natural mode, i.e. the driving force is either buoyancy or wind, sufficient fresh air should be provided to achieve a daily average concentration of carbon dioxide during the occupied period of less than 1500ppm and so that the maximum concentration does not exceed 2,000ppm for more than 20 consecutive minutes each day.
Outside carbon dioxide concentrations are generally around 380ppm. For a typical classroom with 30 students and 2 staff, a fresh air ventilation rate of between 8 and 9 l/s/person corresponds to a carbon dioxide level of around 1000ppm under steady state conditions depending on the ventilation system. A fresh air rate of 5l/s/person corresponds to around 1500ppm.
CIBSE Guide A: Environmental design is the premier technical/reference source for designers and installers of building services, especially low energy and environmentally sustainable buildings.
Table 1.5 has a suggested air supply rate for a number of different building and room types. The majority of the building and room types for example office spaces, restaurants and airports require a minimum fresh air rate of 10 l/s/person.
Part F of the Building Regulations outlines the ventilation rates required for new dwellings. It also provides regulatory guidance for a number of different types of commercial building.
At Ecodraw we use the Dynamic Simulation Modelling (DSM) software EDSL TAS, to create a 3D representation of your building, complete with opening widows and other ventilation devices such as louvres or wind catchers. Different external wind speeds and directions, or no wind at all, can then be simulated to determine how much fresh air will enter the rooms.
The image below is taken from our software and shows in blue arrows where fresh air will enter the building and in red arrows where stale air will exit the building.
For natural ventilated or mixed mode buildings the design of the opening windows, louvres and wind catchers will have a significant impact on the amount of fresh air entering the rooms. To ensure that each of the rooms will receive the correct amount of fresh air to satisfy the appropriate regulations contact us today for a natural ventilation study on your building.
It is best to investigate the natural ventilation of a building in the design stage of your project as retrospectively changing the design or adding in elements such as wind catchers can be costly during the construction phase.
Contact us today if you would like us to carry out natural ventilation calculations on your building.